More Force Review!

Two crates, of mass m1 = 40 kg and m2 = 125 kg, are in contact and at rest on a horizontal surface (Fig. 4-54). A 620 N force is exerted on the 40 kg crate. The coefficient of kinetic friction is 0.15.

All fine so far. The force block 2 exerts on block 1 is equal and opposite to the force block 1 exerts on block 2. To find the force on block 2, you know the acceleration of block 2 and the mass of block 2. This should let you find force on block 2.